Ring scanning antenna adapted for flush mounting



April 16, 1963 B. BERKOWITZ RING SCANNING ANTENNA ADAPTED FOR FLUSH MOUNTING Filed Oct. 4, 1957 I W M w w H H 3 H mg m WW E O W/m MK NW Mm sw N hh \QN 5 A United States Patent 3,086,205 RING SCANNING ANTENNA ADAPTED FOR FLUSH MOUNTING Bernard Berkowitz, New Hyde Park, N.Y., assignor t0 Sperry Rand Corporation, a corporation of Delaware Filed Oct. 4, 1957, Ser. No. 688,812 8 Claims. (Cl. 343754) This invention relates to antennas for radiating or receiving directional microwave energy and more particularly to such an antenna adapted for flush mounting along the skin of an aircraft.

Prior directional microwave radiators for aircraft installation generally include a reflector type antenna mounted in a nose, tail, dorsal, or ventral location. Of these typical antenna locations, the nose and tail locations are not suitable where 360 azimuthal scanning is required. Only the dorsal or ventral positions may be employed. In slower speed aircraft, the increased drag produced by the radome of a dorsal or ventral antenna may be tolerated. However, with the present trend toward higher speed aircraft such radome protrusions result in a prohibitively large penalty in aircraft performance.

A principal object of the present invention is to provide a directional microwave antenna adapted for flush mounting along the skin of an aircraft.

Another object is to provide a flush mounted aircraft antenna adapted to launch directional microwave energy around a full 360 scanning circle.

An additional object is to provide a flush mounted directional antenna adapted to operate with high azimuth scanning rates.

Yet another object is to provide a continuously scanning directional antenna adapted to launch surface-guided waves of electromagnetic energy.

These and other objects of the present invention, as will appear more fully in the following specification, are accomplished in an illustrative embodiment by the provision of an antenna having upper and lower horizontal parallel plate waveguides interconnected by a vertical parallel plate waveguide. The upper and lower walls of the upper and lower waveguides are centrally-apertured circular plates of electrically conductive material. Each of the walls of the interconnecting vertical waveguide defines a surface of generally cylindrical shape, the cylinders being concentric and of different radii. The longitudinal axis of the cylinders coincides with the axes of the centrally-apertured circular plates of the upper and lower waveguides. The vertical waveguide interconnects the entire outer circumferences of the upper and lower waveguides. The inner circumference of the lower waveguide is adapted to receive directional microwave energy; the inner circumference of the upper waveguide is adapted to radiate microwave energy.

Microwave energy received by the lower waveguide is directed along certain geodesics on a surface median to the horizontal plates thereof and into the vertical waveguide. Energy propagates through the vertical waveguide along geodesics on a surface median to the vertical parallel plates thereof and is then directed into the upper waveguide.

In a preferred embodiment of the invention described in detail in the following specification, provision is made to launch surface-guided waves of electromagnetic energy from the inner circumference of the upper waveguide. Such provision includes the addition of a circular plate of electrically conductive material to the inner circumference of the lower plate of the upper waveguide whereby the aperture of said lower plate is completely closed by the conductive material.

A feature of the surface-wave launching embodiment 3,086,205 Patented Apr. 16, 1963 of the invention is that the surface-wave launching means may also serve as an integral radome.

For a more complete understanding of the present invention, reference should be had to the following specification and to the appended drawings of which:

FIG. 1 is an elevational sectional view of one embodiment of the present invention adapted to launch surfaceguided waves of electromagnetic energy, and

FIG. 2 is a cut-away plan view thereof.

In FIG. 1, the lower horizontal parallel plate waveguide is comprised of sheets 1 and 2. As shown in FIG. 2, sheets 1 and 2 are centrally-apertured circular sheets of electrically conductive material. The vertical separation between sheets 1 and 2 is preferably adjusted to be less than a half wavelength at the operating frequency when vertically polarized energy (having electric field vectors perpendicular to sheets 1 and 2) is launched in waveguide 3. For horizontally polarized energy, the vertical separation is preferably adjusted to be more than one half but less than one guide wavelength.

Microwave duct 3 is adapted at a flared end 4 to receive microwave energy emitted from active feed 5. In the illustrative embodiment of FIGS. 1 and 2, feed 5 is adapted to rotate throughout a full 360 in a horizontal plane by means of rotating joint 6, motor 7, and gearing 8. A source of microwave energy (not shown) is coupled to input waveguide 9. Input waveguide 9 is coupled by rotary joint 6 to waveguide 10 which is coupled, in turn, to active feed 5 by flange 11. Active feed 5 preferably comprises a primary rotating horn to which are coupled two auxiliary horns. The phase and amplitude of the electromagnetic energy emitted by the auxiliary horns, for reasons which will appear in the following specification, are adjusted relative to the phase and amplitude of the energy emitted by the primary horn. The primary horn 12 and auxiliary horns 13 and 14 appear in the cut-away plan view of FIG. 2. The auxiliary horns are coupled to the primary horn by means of coupling apertures 15. Half-wave choke 35 facilitates maximum energy transfer from active feed 5 to Waveguide 3.

Sheets 1 and 2 are separated from each other in a vertical plane by tuned posts such as tuned post 16. Post 16 has a central member of appropriate diameter for mechanical support. The inductance of the central member of post 16 is compensated for by the use of capacitive dielectric sleeve 18. The tuned posts thus are adjusted for minimum reflection of microwave energy propagating through duct 3.

An upper horizontal parallel plate waveguide 34 consisting of centrally-apertured conductive sheets 19 and 20 is joined to the lower parallel plate waveguide 3 by means of vertical parallel plate waveguide 22. In the view of FIG. 1, the inner circumference of sheet 19 lies in a plane higher than that of its outer circumference. Waveguide 22 is formed by cylindrically shaped portions of sheets 19 and 2 and sheets 20 and 1. Sheets 19 and 2 and sheets 20 and -1 are respectively interconnected by circular flange 21.

Surface-wave launching means including tapered annular dielectric window 23 and circular conductive mem ber 38 terminates microwave duct 34 in the illustrative embodiment of FIG. 1. Member 38 is dished at its outer circumference to match the curvature of lower sheet 19 of waveguide 34. The flat central portion of member 38 is flush with the upper surface of tapered dielectric 23. The input of window 23 is matched by means of a stepped transition 36 to minimise reflections from the front surface. The tapered dielectric 23 eliminates the need for supporting posts such as post 16 for separating sheets 19 and 20. It will also be seen that dielectric 23 readily serves as a radome by totally enclosing the annular radiating aperture of waveguide 34. Antenna top loading means 24 which may consist of the same dielectric material as dielectric 23 completely covers the central circular region of conductive sheet 19. This top loading means serves to minimize the angle a at which rays of microwave energy such as ray 2S departs from the top surface of the antenna of FIG. 1. The length of dielectric 23 is selected to give a maximum end fire pattern where the length L satisfies the condition that o' d) where a the wavelength in the dielectric and t =the wavelength in air.

That portion of the microwave energy not radiated along rays such as ray 25 are guided across the top surface of the antenna by sheet 19 and top loading means 24 and re-enter waveguide 34 through that portion of dielectric 23 lying diametrically opposite the radial direction of the energy emitted by active feed 5. The reentrant energy then flows through duct 22 and enters the lower horizontal plate waveguide 3 as indicated by the dashed energy fiow arrow 28. A passive feed horn 29 receives the re-entrant energy leaving duct 3 and dissipates such energy in lossy material 30. Passive feed 29 is located at the conjugate feed point of the antenna which lies on the same diameter, but opposite radius as does active feed 5, of the azimuthal scan circle traversed by feed 5. Passive feed 29 is coupled mechanically to rotating waveguide 10 by means of flange 31 and supporting member 32.

As previously mentioned, top loading means 24 serves to minimize the departure angle on which angle is reduced as the thickness of means 24 is increased. However, with a reduction in a, there is a corresponding increase in coupling to the conjugate feed point. The thickness of dielectric top loading means 24 is therefore selected to produce an acceptable compromise between absolute antenna gain (related to the ratio of radiated energy to the energy coupled to the conjugate feed point) and a minimum value of the angle a.

The radial location of the radiating aperture of active feed 5 may be experimentally adjusted so as to produce a relatively fiat phase front of the surface wave launched from the top loading means 24. By holding constant the antenna radius, as measured between the axis of rotating joint 6 and the outer circumference of cylindrical waveguide 22, and the antenna height as measured between the fiat portions of sheets 1 and 20, and by varying the radial position on the radiating end 33 of feed horn 5, an optimum radial length for active feed 5 may be chosen to produce a relatively fiat phase front of the launched surface wave. As is recognized in the art, the directivity of radiated microwave energy is maximized by producing the flattest phase front of such radiated energy.

Representative values for the parameters mentioned which have been successfully employed in one X-band model of the antenna of the present invention are as follows:

Inches Antenna radius 17.75 Antenna height 3.75 Radius of active feed 10.25

It will be noted that because of the different geodesic path lengths traversed by the electromagnetic wave propagating through waveguide 22, the phase front of the wave emitted from dielectric 23 has the shape of a curved surface. This effect is discussed in US. Patent 2,633,533 issued on March 31, 1953, in the name of Charles V. Robinson and in US. Patent 2,653,239 issued on September 22, 1953, in the names of Lan Jen Chu and Charles V. Robinson. However, tapered dielectric 23 acts as a microwave energy lens to partially correct for such wave front distortion.

It was previously mentioned that active feed 5 preferably comprises two auxiliary horns coupled to a primary horn. The need for the auxiliary horns was demonstrated experimentally by first using a single rotating horn and monitoring the azimuthal pattern of the electromagnetic energy radiated by dielectric 23. It was ascertained that first azimuthal side lobes of appreciable intensity, relative to that of the main lobe, were produced using a single feed horn. To improve the azimuthal beam pattern of the radiated energy, the triple feed horn shown in FIGS. 1 and 2 was provided.

In the triple feed horn the phase and amplitude of the energy in the two auxiliary horns 13 and 14 is adjusted, relative to the phase and amplitude of the energy in the primary horn 12, so as to reduce the first side lobes which appear when a single feed horn is utilized. Although the first side lobes may be substantially cancelled by such phase and amplitude adjustment, the second side lobes may be increased in amplitude. Therefore, a compromise must be made in order to obtain the lowest overall side lobe level of the radiated azimuth beam. Tuning screws 37 are located in the horns so as to provide for final adjustments in phase in order to achieve optimum azimuth pattern.

From the preceding specification it will be seen that the objects of the present invention have been accomplished by the provision of a parallel plate antenna adapted to receive microwave energy from a rotatable feed and operative, in one embodiment, to launch said microwave energy in the form of surface-guided waves. The novel design of the antenna facilitates flush installation along the skin of an aircraft thus reducing slip stream drag to an unobjectionable minimum.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. An antenna adapted to launch waves of directional microwave energy, said antenna comprising first, second, and third parallel plate waveguides wherein electromagnetic energy flows along geodesics on a surface median to the parallel plates comprising each waveguide, each of said plates of said first and second waveguides being sheets of electrically conductive material conformable to a circle, each of said plates of said first and second waveguides being disposed relative to the others in a respective parallel plane with at least the two outermost plates being centrally apertured, each of said plates of said third waveguide being of electrically conductive material and conformable to a surface of generally cylindrical shape, the cylinders being concentric and of different diameter, the longitudinal axis of the cylinders coinciding with the axes of the sheets comprising said first and second waveguides, said third waveguide interconnecting the entire outer circumferences of said first and second waveguides, the inner circumference of said first waveguide being adapted to receive directional microwave energy directed thereto through the aperture in said outermost plate thereof, and the inner circumference of said second waveguide being adapted to radiate said microwave energy through the aperture in said outermost plate thereof.

2. Apparatus as defined in claim 1 including a sheet of dielectric material conformable to a circle and having a radius equal to the radius of curvature of the inner circumference of said second waveguide for closing the aperture in that plate of said second waveguide which is more distant from said first waveguide.

3. Apparatus as defined in claim 1 including a source of directional microwave energy adapted to rotate about the axis of said plates comprising said first waveguide for irradiating said inner circumference of said first WEWC- guide.

4. Apparatus as defined in claim 3 further including microwave energy dissipating means connected to said energy source and rotatable therewith for dissipating microwave energy escaping from said inner circumference of said first waveguide at a point diametrically opposite to the point of said inner circumference of said 7 first waveguide irradiated by said energy source.

5. An antenna adapted to launch waves of directional microwave energy, said antenna comprising first, second, and third parallel plate waveguides wherein electromagnetic energy flows along geodesics on a surface median to the parallel plates comprising each waveguide, each of said plates of said first and second waveguides being circular and of electrically conductive material, each of said plates of said first and second waveguides being disposed relative to the others in a respective parallel plane with at least the two outermost plates being centrally apertured, each of said plates of said third waveguide being of electrically conductive material and defining a surface of generally cylindrical shape, the cylinders being concentric and of different diameter, the longitudinal axis of the cylinders coinciding with the axes of the circular sheets comprising said first and second waveguides, said third waveguide interconnecting the entire outer circumferences of said first and second waveguides, the inner circumference of said first waveguide being adapted to receive directional microwave energy directed thereto through the aperture in said outermost plate thereof, and the inner circumference of said second waveguide being adapted to radiate said n1icrowave energy through the aperture in said outermost plate thereof.

6. Apparatus as defined in claim 5 wherein said inner circumference of said second waveguide is terminated by an annular dielectric member.

7. An antenna adapted to launch waves of directional microwave energy, said antenna comprising first, second, and third parallel plate waveguides wherein electromagnetic energy flows along geodesics on a surface median to said parallel plates comprising each waveguide, each of said plates of said first and second waveguides being sheets of electrically conductive material conformable to a circle, each of said plates of said first and second waveguides being disposed relative to the others in a respective parallel plane with at least the outermost plate of said second waveguide and both of said plates of said first waveguide being centrally apertured, each of said plates of said third waveguide being of electrically con ductive material and conformable to a surface of generally cylindrical shape, the cylinders being concentric and of different diameter, the longitudinal axis of the cylinders coinciding with the axes of the sheets comprising said first and second waveguides, said third waveguide in terconnecting the entire outer circumferences of said first and second waveguides, the inner circumference of said first waveguide being adapted to receive directional microwave energy directed thereto through the aperture in said outermost plate thereof, and the inner circumference of said second waveguide being adapted to radiate said microwave energy through the aperture in said outermost plate thereof.

8. An antenna adapted to launch waves of directional microwave energy, said antenna comprising first, second, and third parallel plate waveguides wherein electromagnetic energy flows along geodesics on a surface median to said parallel plates comprising each waveguide, each of said plates of said first and second waveguides being circular and of electrically conductive material, each of said plates of said first and second waveguide being disposed relative to the others in a respective parallel plane with at least the outermost plate of said second waveguide and both of said plates of said first waveguide being cen trally apertured, each of said plates of said third wave guide being of electrically conductive material and dcfining a surface of generally cylindrical shape, the cylinders being concentric and of different diameter, the longitudinal axis of the cylinders coinciding with the axes of the circular sheets comprising said first and second waveguides, said third waveguide interconnecting the entire outer circumferences of said first and second waveguides, the inner circumference of said first Waveguide being adapted to receive directional microwave energy directed thereto through the aperture in said outermost plate thereof, and the inner circumference of said second waveguide being adapted to radiate said microwave energy through the aperture in said outermost plate thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,143 Tinus Apr. 17, 1951 2,633,533 Robinson Mar. 31, 1953 2,653,239 Chu Sept. 22, 1953 

1. AN ANTENNA ADAPTED TO LAUNCH WAVES OF DIRECTIONAL MICROWAVE ENERGY, SAID ANTENNA COMPRISING FIRST, SECOND, AND THIRD PARALLEL PLATE WAVEGUIDES WHEREIN ELECTROMAGNETIC ENERGY FLOWS ALONG GEODESICS ON A SURFACE MEDIAN TO THE PARALLEL PLATES COMPRISING EACH WAVEGUIDE, EACH OF SAID PLATES OF SAID FIRST AND SECOND WAVEGUIDES BEING SHEETS OF ELECTRICALLY CONDUCTIVE MATERIAL CONFORMABLE TO A CIRCLE, EACH OF SAID PLATES OF SAID FIRST AND SECOND WAVEGUIDES BEING DISPOSED RELATIVE TO THE OTHERS IN A RESPECTIVE PARALLEL PLANE WITH AT LEAST THE TWO OUTERMOST PLATES BEING CENTRALLY APERTURED, EACH OF SAID PLATES OF SAID THIRD WAVEGUIDE BEING OF ELECTRICALLY CONDUCTIVE MATERIAL AND CONFORMABLE TO A SURFACE OF GENERALLY CYLINDRICAL SHAPE, THE CYLINDERS BEING CONCENTRIC AND OF DIFFERENT DIAMETER, THE LONGITUDINAL AXIS OF THE CYLINDERS COINCIDING WITH THE AXES OF THE SHEETS COMPRISING SAID FIRST AND SECOND WAVEGUIDES, SAID THIRD WAVEGUIDE INTERCONNECTING THE ENTIRE OUTER CIRCUMFERENCES OF SAID FIRST AND SECOND WAVEGUIDES, THE INNER CIRCUMFERENCE OF SAID FIRST WAVEGUIDE BEING ADAPTED TO RECEIVE DIRECTIONAL MICROWAVE ENERGY DIRECTED THERETO THROUGH THE APERTURE IN SAID OUTERMOST PLATE THEREOF, AND THE INNER CIRCUMFERENCE OF SAID SECOND WAVEGUIDE BEING ADAPTED TO RADIATE SAID MICROWAVE ENERGY THROUGH THE APERTURE IN SAID OUTERMOST PLATE THEREOF. 